When a person starves, their body saves energy by using up immune cells that are not usually needed – especially damaged ones

This means when a person starts eating again their body tells their stem cells to regenerate and rebuild the entire immune system

Fasting two to four days every six months forces body into survival mode

It’s the latest diet fad, with no shortage of celebrity fans.

And now, research claims fasting can be good for your health.

A study found that fasting for two days or more can help to kick-start the immune system, especially if it has been damaged by ageing or cancer treatment.

It encourages the body to replace old and damaged cells, U.S. researchers said.

Valter Longo, longevity expert at the University of Southern California, said: ‘When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged.’

His team found fasting for two to four days every six months forced the body into survival mode, using up stores of fat and sugar and breaking down old cells.

‘The body then sent a signal telling stem cells to regenerate and “rebuild the entire system”.

‘With a system heavily damaged by chemotherapy or ageing, fasting cycles can generate, literally, a new immune system,’ Professor Longo said.

He went on to say: ‘It gives the “okay” for the stem cells to go ahead and begin proliferating – and rebuild the entire system.’

In a pilot trial, cancer patients lost fewer white blood cells if they had fasted for 72 hours before chemotherapy.

Fasting also reduced ill effects and death in mice exposed to chemotherapy drugs and boosted immunity in ageing mice.

Dr Tanya Dorff, a co-author of the research published in the journal Cell Stem Cell, added: ‘While chemotherapy saves lives, it causes significant collateral damage to the immune system.

‘The results of this study suggest that fasting may mitigate some of the harmful effects of chemotherapy.’

The scientists are now exploring the possibility that the same effects of fasting might apply across many biological systems and organs.

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Fasting could be particularly beneficial for people whose immune systems have been damaged by chemotherapy, the researchers say (file picture)